Clarify license

[Balearica]

This repo contains a boilerplate Apache License 2.0 license file, which remains unchanged from the initial commit. However, while that applies to all of the source code in this repo, the built .wasm/.wasm.js files contain a significant number of third party libraries, which use a variety of different license. All of these licenses are permissive, and I believe that are are compatible with distributing Apache 2.0 licensed .wasm/.wasm.js files. However, as several of these programs have attribution requirements, we should be sure that the necessary attributions are included in the npm package.

I reviewed the licenses used by each third-party dependency, and my notes are below.

• Tesseract.js-core source code (any source code in this repo) is Apache-2.0 licensed
• Tesseract is Apache 2.0 licensed
• Leptonica uses the BSD 2-clause license
• libwebp uses the BSD 3-clause license
• giflib uses the MIT license
• zlib uses the zlib/libpng license
  • https://opensource.org/license/zlib
  • This license appears to be less restrictive than the BSD 2-clause license, because it only requires attribution when distributing source code.
    • Attribution when using binaries is requested, but not required: "If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required."
    • There do not appear to be any restrictions on distributing binaries under this license.
• libpng uses the zlib/libpng license
• libjpeg uses the libjpeg license
  • This license appears to be identical in substance to the BSD 2-clause license.
  • https://jpegclub.org/reference/libjpeg-license/
• libtiff uses the libtiff license
  • This license appears to be identical in substance to the BSD 3-clause license.
  • https://libtiff.gitlab.io/libtiff/project/license.html
• openlibm contains code that uses a variety of permissive licenses
  • https://github.com/JuliaMath/openlibm/blob/master/LICENSE.md
  • The only meaningful restriction in any of these licenses is that the copyright notice be provided.